While cargo-handling vehicles and work vehicles mentioned above are running, their front wheels react to the unevenness of the road, causing the body of the vehicle to pitch and bound, thus requiring some control to slow down the running speed. The conventional countermeasures to this kind of problem are, as presented in the Japanese Laid Open Patent No. 63-265024, to equip a vibration-reducing accumulator to the hydraulic cylinder for operating the handling device by means of outside piping through a mode switching valve, and as shown in the Japanese Utility Model Publication No. 60-3159 to provide a balance weight at the rear of the vehicle body through a balancing cylinder. However, both of the conventional systems utilize a hydraulic system and accordingly have poor responsiveness, being unable to preferably control the pitching in spite of their complicated structures. Besides, the conventional systems require such controls as to operate the switching valve, thus having a disadvantage that the booms may be lowered by the switching.